What Causes Frequent Twitching In Thumb?

I am currently experiencing a very strange feeling in my left thumb. From time to time, about every 5 minutes or so, my thumb starts to twitch, or have small convulsions. I am thinking its some form of epilepsy but I have no record of epilepsy. It only starts to to this when I leave it still, but if I type on the computer your use it to do some activity, it never does it. Does anyone have an answer or opinion on the subject? Do I need to have it looked over by a doctor?